The present invention relates to a medical diagnostic method and, in particular, to an in vivo diagnostic method for detecting a blood clot, such as a pulmonary embolism or a thrombus, employing a radiopharmaceutical contrast agent and volume rendering of single photon emission computed tomography (SPECT) images.
Pulmonary embolism is a condition of the lung that emerges when a portion of a blood clot (i.e., thrombus) growing pathologically within a patient breaks off (i.e., embolizes) and travels to the lung. In many instances, the condition itself is immediately life-threatening. However, even when the condition is not immediately life-threatening, a patient presenting with symptoms characteristic of pulmonary embolism must be properly diagnosed to assure that the symptoms do not represent other diseases. Accordingly, detection and localization of pulmonary embolism are critical to insure that the patient receives the appropriate care.
Previously, a technique for diagnosing tumors has been developed. The technique involves localizing a contrast agent at the tumor and obtaining a series of image slices of the tumor using single photon emission computed tomography (SPECT). The image slices are then individually inspected by a physician. As a result, the process is time consuming and expensive.
To improve the ability to diagnose tumors using SPECT, a volume rendering technique has been developed for displaying SPECT data derived from a complete set of image slices through the tumor. According to this technique, a three-dimensional matrix of data is assembled from the image slices. The three-dimensional matrix of data is then scanned along an array of parallel lines at a given angle with respect to the tumor. For each parallel line, the value of the most intense pixel along the parallel line is determined and assigned to a pixel in a two-dimensional array whose position corresponds to the position of the corresponding parallel line in the array of parallel lines. The process is repeated for a series of angles over 360xc2x0 to produce a series of two-dimensional images. When the series of two-dimensional images are displayed sequentially, a rotating view of the most intense pixels is produced.
In spite of the foregoing, the utility of SPECT as a tool for diagnosing pulmonary embolism remained limited. The limited use of SPECT in connection with pulmonary embolism is due, at least in part, to the fact that the normal anatomy of the thorax is complex. As a result, structures highlighted by the contrast agent are variable, often in a pattern that is unfamiliar to physicians, and without the normal identifying landmarks. Thus, the location of the thrombus and the extent of disease was expected to be difficult to ascertain from the SPECT images, even if volume rendering techniques were employed.
Accordingly, it would be highly beneficial to provide a method for identification and localization of pulmonary embolism using SPECT wherein a three-dimensional representation of a thrombus is obtained. The three-dimensional representation of the thrombus should enable a physician to more clearly, accurately, and efficiently determine the extent of disease. Accordingly, the present invention should provide a significant qualitative improvement in the ability of a naive physician to identify and localize a thrombus.
The shortcomings associated with the known methods for localization of blood clots are overcome to a large degree by a method in accordance with the present invention. The method according to the present invention comprises the step of localizing a radiolabelled compound at a thrombus by administering a radiopharmaceutical compound to the patient. Two-dimensional images representing a physical property associated with the radiolabelled thrombus, such as single photon emission computed tomography (SPECT) images, are then acquired and assembled into a three-dimensional matrix of data. The three-dimensional matrix of data is then scanned along an array of parallel lines to determine a maximum value along each line. The maximum value along each line is then assigned to a pixel in a two-dimensional array, where the relative position of the pixel in the two-dimensional array corresponds to the relative position of the line in the array of parallel lines. The three-dimensional matrix of data is optionally scanned along additional arrays of parallel lines to produce a series of images of the thrombus as viewed from different angles. The series of images can be displayed sequentially to produce a rotating view of the thrombus.